Reservoir Management

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Fish Population Surveys

TWRA reservoir biologists spend many hours each year monitoring sport fisheries and forage fish communities. Because looking at the entire population of fish in a lake is virtually impossible, biologists must depend on sampling to get a snapshot of population status and make predictions about how it will look in the future. Different sampling methods (electrofishing, nets, trawls) are used to sample fish populations. Targeted species surveys may be conducted to obtain information about fish population size structure, recruitment, growth, density, and mortality.

Information gathered from sampling surveys is coupled with information about the human and habitat components of sport fisheries and used to make management recommendations for harvest restrictions and/or stocking. Hatchery managers also use these gears to collect broodstock from wild populations which can be used in hatcheries to produce fish for stocking. The following section briefly describes sampling gear used by TWRA reservoir fisheries and hatchery staff.   

Boat mounted electrofishers are used in Tennessee reservoirs to fulfill various sampling objectives.

Bass, crappie, and sunfish are highly vulnerable to this gear and surveys are normally conducted during the spring months.

A sampling design is chosen which reflects habitat diversity within a lake and fish are collected after being stunned by the shocking boat's electrical field.

Dip netters at the front of the boat pick up the fish and hold them in livewells for later analyses.

Gill nets are used for a variety of fish species that are difficult to sample with electrofishing gear.

TWRA uses them to collect sauger, walleye, white bass, striped bass, and Cherokee bass.

Most netting surveys are conducted during the winter months and may be targeted at pre-spawn runs.

Like other sampling methods gill net samples yield important insight into natural spawning success, success of stocking programs, and sizes of fish available to anglers.

Like electrofishing, seining is an active sampling method that allows biologists to look at forage availability, and survival of young sport fish.

Seines are really long, fine-meshed nets that are dragged through the water in shoreline areas.

Seine hauls have also been used by TWRA to evaluate stocking success of striped bass.

Often the work does not stop in the field for TWRA reservoir crews.

Fish samples often must be processed in the lab, species identified, and counted.

In addition, otoliths (ear bones) are routinely used by TWRA biologists to determine age structure and growth rates for sport fish populations.

Data must be entered into computer databases, analyzed, and summarized for reports.

The scenes below illustrate some of these activities.

Larval Fish From Neuston Net Sample
Reading Otoliths Under a Microscope

 Fisheries Habitat

The term “habitat” refers to all components of the environment necessary for fish to spawn, breed, feed and grow to maturity. Many parts of the environment contribute to healthy fish habitat including water quality, water level regimes, nutritional inputs in the form of critical chemical elements, cover for young fish and predators, and substrate for production of various invertebrates which contribute to the complex food chain in a fishery. Maintenance of healthy fish habitat is necessary to ultimately produce productive fish populations with favorable growth, abundance, and size characteristics which are beneficial for Tennessee anglers. In addition to monitoring fish populations, TWRA biologists also monitor water quality and enhance habitat through the installation of structures to improve physical stability and complexity of the environment. As reservoirs age in Tennessee, much of the physical habitat which was present at impoundment is lost to natural degradation. Stands of trees eventually erode and other structures such as roadbeds, rock walls, and natural outcropping can become covered by sedimentation. 

Fish require water which is not only clean of pollutants that can be toxic to fish, but also contain chemical nutrients which are necessary to produce the microscopic plants, bacteria, and invertebrates that are the primary producers in the food chain that fish need to survive and grow. Temperature and dissolved oxygen also play a critical role in fish health. TWRA biologists monitor dissolved oxygen and temperature throughout the water column in reservoirs during the warm summer months. This information is used to determine the depth of the thermocline, as well as assess the suitability of the seasonal temperature and oxygen levels for predicting fish distribution and also growth and survival of recently hatched fish. In the unfortunate case of fish kills, the temperature/dissolved oxygen profiles often provide an understanding of the root cause of the kill.

Although sedimentation is a natural process that occurs within reservoirs, activities within the watershed have a profound effect on the rate of sediment which enters a reservoir. Suspended soil particles entering a reservoir can cause turbidity in the water column as well as settle out thus covering spawning habitat and other physical structures within a reservoir. Reduced water clarity from suspended inorganic particles can reduce the ability of sunlight to penetrate the water column, in turn, reducing the depth at which phytoplankton (i.e. microscopic plants) and can exist. These single cell microscopic plants are the beginning of the food chain and their abundance directly affects fish abundance. Reduced depth of sunlight also reduces the ability of larger rooted plants to grow. Monitoring land use practices and its effects on water clarity is an important component of reservoir fisheries management. Often measures are taken to stabilize shoreline areas and provide sediment traps before it can enter a reservoir.

The TWRA has attempted multiple projects to establish native aquatic plants. Many of these have been successful and are ongoing, while others have proved ineffective. Cypress tree plantings have been quite successful in many reservoirs and the established tree stands serve to trap sediment and stabilize shorelines. The roots on mature trees can also serve as nursery cover for small fish during times of inundation.

"Planted stand of bald cypress trees at J. Percy Priest"

Shoreline cultivation of grasses has been used to stabilize shoreline and also provide nursery habitat. Grasses can be planted by harrowing and broadcasting or by hydroseeding, during winter months when lakes are drawn down to winter pool. Once the grass becomes established prior to inundation in the spring, they provide nursery habitat for juvenile fishes. The grasses eventually die back but not before providing cover for small fish early in their life cycle. Hydroseeding has been used recently on Boone reservoir to establish shoreline vegetation on the exposed littoral zone. In addition to future nursery habitat, this also serves to protect the exposed shoreline while Boone is being held at a low pool for several years for repairs to the dam.

Hydroseeding exposed shoreline on Boone Reservoir

Reservoirs in Tennessee range in age from almost 40 years to over 100 years old. As reservoirs age, natural woody cover such as standing timber are lost to decomposition. Other physical features such as rock walls and road beds also degrade with time or can become covered with sediment. To replace the intrinsic cover lost over time, TWRA biologist install fish attractors using both natural materials and artificial materials. An ongoing debate has been whether fish attractors simply attract fish or actually raise the net production of fish in a reservoir. In truth, all fish attractors probably have some degree of both of these benefits.

Natural materials include mostly woody debris, such as brush piles, trees, and wooden stake beds, to attract larger fish as well as provide cover for juvenile fish and prey fish. The advantage to natural materials is they are readily adapted by cover oriented fish species, they eventually decompose leaving no synthetic materials in the environment, and they are readily colonized by invertebrates providing a food source for juvenile fishes. As woody materials decompose they also provide food for bacteria and other microscopic organisms. The biggest disadvantage to natural materials is the need to replace the materials frequently due to degradation.

“Christmas trees placed on shoreline during winter drawdown”
“Stake beds being installed during winter drawdown to attract crappie”
“Deepwater fish attractor made from native cut trees”

In addition to fish attractors made from natural materials, the TWRA also installs fish attractors made from artificial materials including plastic and concrete. The biggest advantage of these materials over woody debris is the longevity of the structure which can last for decades. Although not as easily colonized by aquatic invertebrates as woody materials, with time most plastic and concrete materials will become colonized with these important food items. The materials used are often dictated by availability and cost.

“Drain pipe fish attractors placed under a fishing pier at Normandy Reservoir”
“Concrete reef balls being constructed in East Tennessee”
“Catfish spawning habitat made from recycled plastic barrels”

In addition to fish attractors made completely from either natural or synthetic materials, many of the installations are composites of both types of materials. These structures have the advantage of being readily colonized by invertebrates and juvenile fish while having a lifespan greater than natural materials alone.

“Spawning bench made from sawmill slabs and concrete block provide spawning cover for smallmouth bass and sunfish”
“Fish tree made from wooden post and surplus plastic gas pipe”
“Composite fish attractors made from recycled plastic pallets and Christmas trees”

Many reservoirs in Tennessee have fish attractor locations listed on online maps. These maps are available at this link:

Tennessee anglers often want to know if they are allowed to place their own fish attractors in public waters.

Fish attractor installations are allowed, but permits are required by either the Tennessee Valley Authority (TVA) or the United States Army Corps of Engineers (USACE) depending on which agency has operational jurisdiction over a given reservoir or river. Allowable materials and locations of angler-installed fish attractors are specified by the permits.


For waterbodies regulated by the Army Corps of Engineers, the Resource Managers' office should be contacted for each specific reservoir. Below is a list of contacts by location:

Center Hill Reservoir: Center Hill Lake Resource Manager’s Office (931) 858-3125

Cordell Hull Reservoir:

Cheatham Reservoir:

Dale Hollow Reservoir: Dale Hollow Lake Resource Manager's Office 931-243-3136

J. Percy Priest Reservoir:

Old Hickory Reservoir:

Angler  Surveys

Fisheries management in Tennessee is based on information collected with sound methodology using the most contemporary techniques available within the community of fisheries professionals. Although the methods we use for obtaining information are sound and proven, there is no way to circumvent the inherent variability common to biological data. It is, however, possible to validate our findings by comparing the results of multiple techniques. Commonly, we use angler surveys to complement fish community surveys.

Angler surveys rely on fishermen to provide information about a fishery including, effort, catch, preferences, demographics, and economics. The information we collect through angler surveys gives us an unbiased sample of the angling population that we use in addition to our fishery independent assessments to select the best management plans to accommodate the widest variety of anglers. 

Just as no single sampling method can be used to describe every fish population, (see fish community surveys), no single angler survey method can adequately represent all anglers or all components of a fishing experience. We therefore use several angler survey techniques to gain a comprehensive picture of the sportfishing population in Tennessee. The methods are described below:

The TWRA contracts annually with the University of Tennessee (UT) to do an annual random survey of licensed anglers.

A list of licensed anglers is provided to the Human Dimensions Research Lab at UT. From that list, a large random sample of anglers is contacted by telephone. The anglers are asked questions such as where they live, where they like to fish, the type of fishing they do, which species they like to fish for, and their satisfaction with fishing in Tennessee. The anglers are also invited to provide comments and suggestions concerning the management of Tennessee Fisheries. 

The Advantages of this type of survey are:

  1. Provides unbiased randomly collected information about the entire angling population in Tennessee.
  2. Low cost per interview
  3. Good response rates

The Disadvantages Include:

  1. Recall Bias - This means that an angler may be asked questions about a fishing experience that occurred weeks maybe even months before the interview. The angler may not be able to accurately answer all of the questions due to the passage of time.
  2. A particular portion of the angling population may choose to not respond

Each year representatives from the TWRA approach anglers while they are fishing in order to ask them about their fishing experience that day. This process is known as a creel survey.

The "creel clerks" ask anglers questions about the amount of time they have been fishing, what they are fishing for, what they have caught or released, where they are from, and questions about how much money was spent on the fishing trip. The information obtained is very useful to TWRA fishery biologists to make informed decisions regarding the management of the state's resources. 

Currently, the TWRA employs 11 full-time creel clerks who conduct creel surveys on 17 reservoirs throughout Tennessee. Annually they collect between 10,000 and 15,000 interviews. In addition to reservoirs, various seasonal stream and tailrace surveys are conducted on an as-needed basis. The TWRA also contracts with the Tennessee Technological Institute from time to time to conduct specialized surveys where new research is the main focus.

The creel clerks may approach anglers by boat while they are in the process of fishing. This type of survey is known as a "roving creel survey". At other times the creel clerk may wait at a boat ramp, or pier to interview anglers at the completion of a fishing trip. This is known as an "access point creel survey". If you are approached by a creel clerk, please take a few minutes to respond to an interview. This process allows you to have a voice in the management of Tennessees' fishery resources.

Advantages of Creel Surveys:

  1. No recall bias - anglers are not required to remember effort and catch from past fishing events
  2. High response rates
  3. Creel clerks are able to directly observe caught species. This allows for accurate identification and measuring of harvested fishes.

Disadvantages of On-Site Creel Surveys:

  1. It can be difficult to relate the information to the entire fishing population. For example, a reservoir creel survey would not represent stream or pond anglers.
  2. High cost per interview

The Tennessee Wildlife Resources Agencys' BITE (Bass Information from Tournament Entries) program is a coordinated effort between the Agency and organized bass clubs that hold fishing tournaments in Tennessee.

Tournament organizers voluntarily submit their tournament data to the TWRA Fisheries Management Division via an online reporting form or a mail-in tournament report card. The information on the report form or card supplies information such as the location of the tournament, number of participants, total catch, and size and weight structure of the tournament catch. Annually, the information collected from tournament organizers is compiled into a report that benefits both the TWRA as well as tournament anglers.

The Advantages include:

  1. Information about bass stocks is compiled for major reservoirs 
  2. Information about otherwise unknown tournament efforts is provided to biologists
  3. Tournament anglers benefit by receiving information about bass tournament catches around Tennessee.

Disadvantages include:

  1. Information is provided only for a very specific portion of the fishing population.
  2. Catch, effort, and size structure may be proportionally greater than in the general fishing population 
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